The present invention relates to semiconductor equipment or semiconductor devices and an apparatus for manufacturing semiconductor devices, and particularly to a vacuum heating furnace in which a treated object retained within a chamber is treated by heating or the like.
As an apparatus for manufacturing semiconductors and semiconductor devices, heretofore, there is a vacuum heating furnace in which a silicon semiconductor wafer retained within a quartz chamber is heated by radiation heat radiated by a lamp or a heater from the outside of the chamber and an oxide film layer is deposited on the surface of the semiconductor wafer by introducing oxygen gas into the chamber.
In the semiconductor element or semiconductor device, in order to reduce an electric power consumed when the semiconductor element or semiconductor device is operated or in order to improve an operating speed by suppressing a calorific value, it is requested that the semiconductor element should be microminiaturized. Recently, a technology for microminiaturizing semiconductor elements makes a rapid progress, and there is an increasing demand of further microminiaturizing the semiconductor elements. Also, a semiconductor device having a new structure such as a flash memory has appeared, and is now commercially available on the market. With respect to these new semiconductor devices, there is still an increasing demand of increasing a memory area. To meet with these requirements, it is requested that an oxide film on a semiconductor wafer should have a thickness as very thin as about several nanometers.
To this end, a temperature at which the semiconductor wafer is heated should be very high in a range of from about 900.degree. C. to 1000.degree. C. or higher. At the same time, it is necessary to reduce a time for heating the semiconductor wafer as much as possible. That is, during the time when the semiconductor wafer is heated at a rising temperature, the process for depositing the oxide film continues, thereby making it difficult to deposit a thin homogeneous oxide film on the semiconductor wafer.
Therefore, in order to heat a semiconductor wafer in a period of time as short as possible, it is customary that a semiconductor wafer is directly heated by the irradiation of radiation light emitted from a halogen lamp or a heater, for example, from the outside of a quartz chamber. According to this technology, although energy of radiation light is contained in infrared rays of light having a wavelength of about 2 to 3 .mu.m, light of this wavelength is not absorbed by quartz which is a material of the quartz chamber. Thus, the radiation light cannot heat the quartz. Having passed the quartz chamber, the radiation light reaches the semiconductor wafer, in which it is absorbed, thereby resulting in the semiconductor wafer being heated.
However, when this radiation light passes the quartz chamber, the radiation light is propagated through the quartz material while a part of the radiation light is being reflected on the surface of the quartz, and reaches a portion distant from a light incident point. That is, it was understood that the quartz chamber plays a role of an optical waveguide.
Then, light that passed the inside of the material of the quartz chamber heats and deteriorates an assembly mounted on the surface of the quartz chamber.
For example, in order to seal the quartz chamber in the vacuum state, an O-ring made of a high-molecular compound such as a fluororubber is used as a connection portion which is connected to another chamber. The reason for this is that a soft and flexible material such as a high-molecular compound should be used to seal a material such as a quartz which tends to be cracked. However, it is to be noted that such a soft and flexible material is generally not satisfactory in heat-resisting property. A heat-resisting property of the above-mentioned high molecular compound is such one that the high molecular compound is denatured at a temperature up to about 300.degree. C. at most. If the high molecular compound is heated at a temperature higher than the above-mentioned temperature, then the quality of the material of the high molecular compound is deteriorated, and hence cannot be used to seal the quartz chamber in the vacuum state.
JP-A-2-268420 describes a technology in which a part of quartz chamber is made opaque in order to reduce light transmitted through the inside of the quartz chamber. According to this conventional technology, a part of a furnace tube which is the quartz chamber is made of an opaque quartz, whereby light transmitted through that opaque quartz portion to the O-ring is shielded. Similarly, JP-A-3-67499 describes a technology in which a part of quartz tube is made of an opaque material in order to prevent light radiated from plasma generated in the inside of the quartz tube from propagating the inside of the quartz tube to heat the O-ring.
Furthermore, JP-A-64-44016 describes a technology in which a transmitted light shielding plate is embedded into the inside of the material of the quartz tube.
However, if a chamber is made of a quartz material and an opaque quartz material, then there arises a problem that a mechanical strength of the chamber is weakened.
Showing an example in which physical characteristics of quartz and opaque quartz are compared with each other, a viscosity of quartz glass is 400 GPa.cndot.s for a transparent quartz at 1200.degree. C. and 74 GPa.cndot.s for an opaque quartz. A compressive strength of a rod-like test sample having a diameter of 24 mm at a room temperature is 1130 Mpa for a transparent quartz and 268 Mpa for an opaque quartz. Further, at a room temperature, a bending strength of a transparent quartz is 46.5 Mpa and that of an opaque quartz is 15.8 Mpa. A temperature in which a flexibility occurs as a viscosity is lowered with an application of heat during a long period of time is 1100.degree. C. for a transparent quartz and 1050.degree. C. for an opaque quartz. As described above, mechanical strengths of the two materials are different from each other considerably.
To make one chamber, two materials should be jointed by a suitable method such as welding or bonding. In the above-mentioned conventional technologies, there have not yet been considered such problems in which a stress occurs in the joint portion of the two materials having different mechanical strengths due to a difference of physical property so that, when the joint portion is heated at an increasing temperature, the joint portion is cracked or an internal stress is accumulated.
Specifically, by using different materials, it is very difficult to make a furnace body in which a semiconductor wafer is heated at a temperature which increases rapidly from a strength reliability stand-point. Further, it is needless to say that, if the whole of the chamber is made of the opaque quartz, then light may not reach the semiconductor wafer retained within the opaque quartz chamber.
Although a technology in which the mounted portion of the O-ring is cooled by a suitable method such as a water cooling, there is a limit in cooling the mounted portion of the O-ring by a heat conduction, which hinders a lamp or a heater from increasing its output power.
Furthermore, when a water cooling pipe or the like is laid, a leakage water countermeasure also becomes necessary. There arise problems from an equipment cost standpoint and a production cost standpoint.
When the very thin oxide film is deposited on the semiconductor wafer by rapidly heating the semiconductor wafer, there still remain the problems as described above. As a result, the output of the heater cannot be increased and a temperature rise speed is limited, which as a result imposes a restriction on making the oxide film very thin. Even though the performance of the flash memory or the like is considerably affected by various factors such as a thickness of an oxide film and a homogeneity of a film quality, it is unavoidable that a device performance is limited by the above-mentioned problems.